HEAD-Sonic Pro Tennis String Reel Black-() Designed to improve elasticity, Head Sonic Pro has a combination of properties, which allows the string to remain durable, while providing additional power and depth in comparison to the typical polyester-based strings. Now available in a space saving reel, Sonic Pro provides excellent response without sacrificing a great deal of durability... Size - (See Description) | Color - (See Description) Authorized Head Dealer. All racquets are strung and ready for the courts! SEE SELLER DETAILS FOR RETURN POLICY.